This invention relates to a spool valve such as an oil valve for an automatic transmission, which is integrated into a hydraulic control circuit of an automatic transmission or the like of an automobile and conducts switching of oil passage, and a process for manufacturing the same.
In a conventional spool valve to be used as an oil valve for an automatic transmission or the like, it is common that a rod-shaped material 20 made of a metal as shown in FIG. 10 is cut by a lathe or the like, and a shaft 21 on which a valve body is carved out is prepared as shown in FIG. 11. Therefore, there are problems that a large amount of a material is cut and wasted as chips, and time is required for machining of material thus lowering productivity. Moreover, in order to give abrasion resistance to such a shaft, after machining of material, it is necessary to subject the whole surface of the shaft to a carburization quenching processing as shown in FIG. 12. However, due to the carburization quenching processing, thermal strain of the shaft is necessarily induced, so that after carburization quenching processing, it is necessary to subject it to straightening as shown in FIG. 13. Thus, there are problems that productivity is low, and cost is high.